We propose to investigate the following effects of lead in rat and mouse kidney: (1) simulation of cell proliferation in the proximal convoluted tubules and its significance for carcinogenesis: (2) induction of specific cytoplasmic fibrillar protein in proximal tubular epithelial cells by small doses of lead and the possible significance of this protein as a detoxifying agent: (3) the evolution of ultrastructural lesions caused by lead in proximal tubular epithelium.